US residential 120/240 volt electrical installations use two, 180-degree anti-phase 120 volt supplies, either of which can power 120-volt loads, while 240-volt loads are powered by connecting them between the anti-phase 120-volt lines, giving 240 volts line-to-line. Such a supply is called a “split-phase” supply.
Sometimes, an alternative energy source may only provide a single phase 120 volt supply; the other phase then having to be generated from this single phase by use of a phase-inverting transformer, such as a center-tapped auto-transformer.
For example, a back-up supply using a single phase 120-volt inverter such as Xantrex type SW4048 may need a phase-inverting transformer to supply the other phase required for powering 240 volt loads.
Other inverters may provide a 240 volt floating supply and require a center-tapped auto-transformer to balance the 240 volts relative to ground to obtain the two anti-phase 120-volt hotlegs.
The size, weight and cost of the auto-transformers mentioned above rise with power rating, due to the need for large iron cores and many-turn, thick copper windings. Moreover, a conventional transformer entails a small, but still possibly significant, continuous power loss due to hysteresis in the iron core, even when there is no load. Therefore there is a need for alternative techniques to provide split-phase supplies from single-phase supplies with reduced size, weight, cost and no-load power loss.